As mobile devices have been increasingly developed, and the demand for such mobile devices has increased, the demand for secondary batteries has also sharply increased. Among such secondary batteries is a lithium secondary battery exhibiting high energy density and operating voltage and excellent preservation and service-life characteristics, which has been widely used as an energy source for various electronic products as well as for the mobile devices.
However, various combustible materials are contained in the lithium secondary battery. As a result, there is a possibility of danger in that the lithium secondary battery will be heated or explode due to overcharge, overcurrent or any other external physical impacts. In other words, the lithium secondary battery has low safety. Consequently, safety elements, such as a positive temperature coefficient (PTC) element and a protection circuit module (PCM), to effectively control an abnormal state of the lithium secondary battery, such as overcharge or overcurrent, are mounted in the lithium secondary battery in a state in which the safety elements are connected to a battery cell of the lithium secondary battery.
Generally, the PCM is connected to the battery cell via conductive nickel plates by welding or soldering. That is, nickel plates are connected to electrode tabs of the PCM by welding or soldering, and then the nickel plates are connected to electrode terminals of the battery cell by welding or soldering. In this way, the PCM is connected to the battery cell, thereby manufacturing a battery pack.
It is necessary for safety elements, including such a PCM, to be maintained in electrical connection with electrode terminals of a battery cell and, at the same time, to be electrically isolated from other parts of the battery cell. A plurality of insulative mounting members or a plurality of parts is necessary to achieve such connection with the result that a process of assembling a battery pack is complicated, and the size of a space to receive the battery cell is reduced.
Also, a plurality of welding or soldering processes is required to constitute a battery pack. Such welding processes must be carried out with high precision because the structure of the secondary battery is very small with the result that a defect ratio may be increased. Furthermore, such processes are added to manufacture a product with the result that manufacturing cost of the product is increased.
Therefore, it is possible to modify the upper structure of the battery cell so that the electrode terminals can be mechanically coupled and electrically connected to the PCM. In this case, it is possible to reduce the number of parts disposed at the top of the battery cell and to manufacture a battery pack in a structure in which the PCM and the top cap are sequentially connected to the protruding electrode terminals.
However, the structure in which the electrode terminals are modified requires the battery cell to be newly designed. For this reason, a conventional battery cell manufacturing process and a conventional battery pack manufacturing process must be changed with the result that the manufacturing cost is increased.
Consequently, there is a high necessity for technology to reduce the number of members mounted to the top of the battery cell while using a conventional battery cell and maximally utilizing a conventional assembly method, thereby simplifying an assembly process, to reduce the number of welding processes, thereby minimizing a defect ratio during the assembly of battery cells, to achieve stable coupling between members disposed at the top of the battery cell, and to increase the capacity of the battery cell.